This application claims the priority of Japanese Patent Application No. 4-81662, filed on Mar. 2, 1992, which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to electronic endoscope apparatus using a circuit board having a cavity and, more particularly, relates to the circuit construction for electrically isolating a patient circuit on the electronic endoscope side from an output circuit.
2. Description of the Related Art
An electronic endoscope apparatus is conventionally known, for observing the interior of a body cavity such as the alimentary canal by means of CCD (Charge Coupled Device) provided at the terminal end thereof to form a solid image pickup device. In this type of electronic endoscope apparatus, an internal image of the subject to be observed (patient) picked up by the above CCD may be captured by inserting the electronic endoscope (electronic scope) into the body cavity, whereby such as examination and diagnosis may be conducted while observing the image displayed on a monitor.
FIG. 4 schematically shows the construction of an electronic endoscope apparatus of this type. This apparatus is constructed to have an electronic endoscope which is connected to an external processor unit. As shown in the figure, a patient circuit 2 is disposed on the circuit board 1 in the electronic endoscope apparatus in such a manner that it is connected to an output circuit (secondary circuit) 4 via an isolation device 3. Specifically, the patient circuit 2 and the output circuit 4 include such components as: the above CCD; CCD driver; a signal processing circuit for performing image processing such as gamma-correction with respect to the video signal obtained at the CCD; A/D converter; D/A converter; and a memory; and the isolation device 3 is placed at one of the in-between positions in the course of these circuits. Accordingly, those circuits toward the electronic endoscope from the isolation device 3 constitute the patient circuit 2 while the circuits on the external processor unit side or the monitor side constitute the output circuit 4. Here, a photocoupler or a pulse transformer for example is used as the isolation device 3 so as to maintain a dielectric strength of 3.about. 4 kV or more by the isolation device 3, thereby securing the safety of the electronic endoscope for the patient.
In the above conventional electronic endoscope apparatus, however, though as described a predetermined electrical insulation at the signal transmission lines is maintained by the isolation device 3, it is possible that a current flows to the patient circuit 2 from the output circuit 4 in a manner of detouring around through the circuit board 1, causing a problem that the dielectric strength is not completely maintained. In other words, as indicated by chain line 100 in FIG. 4, a flow passage of current to the wiring portion of the patient circuit 2 from the wiring portion on the side of the output circuit 4 is formed through the circuit board 1 at the outside of the attaching portion of the isolation device 3, whereby isolation of the patient circuit from the output circuit by the isolation device 3 does not make sense.
An arrangement may be taken into consideration to maintain the dielectric strength at the circuit board 1, in which the distance on the circuit board 1 between the patient circuit 2 and the output circuit 4 is increased in the state where the isolation device 3 is floated (isolated for example by an insulating material) from the circuit board 1. In such a case, however, the circuit board 1 itself becomes larger and more complicated in construction, resulting in a disadvantage that the size of the apparatus is increased.